introduction to mobile communications tcom 552, lecture #10 hung nguyen, ph.d. 13 november, 2006

Introduction to Mobile Introduction to Mobile CommunicationsCommunications

TCOM 552, Lecture #10Hung Nguyen, Ph.D.13 November, 2006

11/13/2006Hung Nguyen, TCOM 552, Fall 20062

OutlineOutline

Cordless Systems and Wireless Local Loop (Chapter 11)

Mobile IP and Wireless Application Protocol (Chapter 12)

Cordless System Operating Cordless System Operating EnvironmentsEnvironments

Residential – a single base station can provide in-house voice and data support

Office– A single base station can support a small office– Multiple base stations in a cellular configuration

can support a larger office Telepoint – a base station set up in a public

place, such as an airport. Has not succeeded in the market.

Design Considerations for Cordless Design Considerations for Cordless StandardsStandards

Modest range of handset from base station (up to 200 m), so low-power designs are used

Inexpensive handset and base station, dictating simple technical approaches

Frequency flexibility is limited, so the system needs to be able to seek a low-interference channel whenever used

Digital Enhanced Cordless Telecom & Digital Enhanced Cordless Telecom & Personal Wireless TelecomPersonal Wireless Telecom

Time Division Duplex (TDD)Time Division Duplex (TDD)

TDD also known as time-compression multiplexing (TCM)

Data transmitted in one direction at a time, with transmission between the two directions– Simple TDD (Simplex)– TDMA TDD

Simplex TDD TransmissionSimplex TDD Transmission

Simple TDD (Simplex)Simple TDD (Simplex)

Bit stream is divided into equal segments, compressed in time to a higher transmission rate, and transmitted in bursts

Effective bits transmitted per second:

R = effective data rate B = size of block in bits Tp = propagation delay Tb = burst transmission time Tg = guard time

gbp TTTB

Simple TDD (Simplex)Simple TDD (Simplex)

Actual data rate, A:

Combined with previous equation:

The actual data rate is more than double the effective data rate seen by the two sides

TDMA TDD (Time Slots)TDMA TDD (Time Slots)

Wireless TDD typically used with TDMA– A number of users receive forward channel

signals in turn and then transmit reverse channel signals in turn, all on same carrier frequency

Advantages of TDMA/TDD:– Improved ability to cope with fast fading– Improved capacity allocation

DECT Protocol ArchitectureDECT Protocol Architecture

Physical layer – data transmitted in TDMA-TDD frames over one of 10 RF carriers

Medium access control (MAC) layer – selects/ establishes/releases connections on physical channels; supports three services:– Broadcast– Connection oriented– Connectionless

Data link control layer – provides for the reliable transmission of messages using traditional data link control procedures

DECT Protocol ArchitectureDECT Protocol Architecture

Differential QuantizationDifferential Quantization

Speech signals tend not to change much between two samples– Transmitted PCM values contain considerable

redundancy Transmit difference value between adjacent

samples rather than actual value If difference value between two samples

exceeds transmitted bits, receiver output will drift from the true value– Encoder could replicate receiver output and

additionally transmit that difference

Differential PCM (DPCM)Differential PCM (DPCM)

Since voice signals change relatively slowly, value of k-th sample can be estimated by preceding samples

Transmit difference between sample and estimated sample– Difference value should be less than difference

between successive samples At the receiver, incoming difference value is

added to the estimate of the current sample– Same estimation function is used

Adaptive Differential PCM (ADPCM)Adaptive Differential PCM (ADPCM)

Improve DPCM performance using adaptive prediction and quantization– Predictor and difference quantizer adapt to the

changing characteristics of the speech Modules

– Adaptive quantizer– Inverse adaptive quantizer– Adaptive predictor

ADPCM Encoder & DecoderADPCM Encoder & Decoder

Subject Measurement of Coder Subject Measurement of Coder PerformancePerformance

Subjective measurements of quality are more relevant than objective measures

Mean opinion score (MOS) – group of subjects listen to a sample of coded speech; classify output on a 5-point scale

MOS scale is used in a number of specifications as a standard for quality

Wireless Local Loop (WLL)Wireless Local Loop (WLL)

Wireless Local LoopWireless Local Loop

Wired technologies responding to need for reliable, high-speed access by residential, business, and government subscribers– ISDN, xDSL, cable modems

Increasing interest shown in competing wireless technologies for subscriber access

Wireless local loop (WLL)– Narrowband – offers a replacement for existing

telephony services– Broadband – provides high-speed two-way voice

and data service

WLL ConfigurationWLL Configuration

Advantages of WLL over Wired Advantages of WLL over Wired ApproachApproach

Cost – wireless systems are less expensive due to cost of cable installation

Installation time – WLL systems can be installed in a small fraction of the time required for a new wired system

Selective installation – radio units installed for subscribers who want service at a given time– With a wired system, cable is laid out in

anticipation of serving every subscriber in a given area

Propagation Considerations for WLLPropagation Considerations for WLL

Most high-speed WLL schemes use millimeter wave frequencies (10 GHz to about 300 GHz)– There are wide unused frequency bands

available above 25 GHz– At these high frequencies, wide channel

bandwidths can be used, providing high data rates

– Small size transceivers and adaptive antenna arrays can be used

Propagation Considerations for WLLPropagation Considerations for WLL

Millimeter wave systems have some undesirable propagation characteristics– Free space loss increases with the square of the

frequency; losses are much higher in millimeter wave range

– Above 10 GHz, attenuation effects due to rainfall and atmospheric or gaseous absorption are large

– Multipath losses can be quite high

Fresnel ZoneFresnel Zone

How much space around direct path between transmitter and receiver should be clear of obstacles?– Objects within a series of concentric circles around the line of

sight between transceivers have constructive/destructive effects on communication

For point along the direct path, radius of first Fresnel zone:

Atmospheric AbsorptionAtmospheric Absorption

Radio waves at frequencies above 10 GHz are subject to molecular absorption– Peak of water vapor

absorption at 22 GHz– Peak of oxygen

absorption near 60 GHz

Favorable windows for communication:– 28 GHz to 42 GHz– 75 GHz to 95 GHz

Effect of RainEffect of Rain

Attenuation due to rain– Presence of raindrops can severely degrade the

reliability and performance of communication links

– The effect of rain depends on drop shape, drop size, rain rate, and frequency

Estimated attenuation due to rain:

A = attenuation (dB/km) R = rain rate (mm/hr) a and b depend on drop sizes and frequency

Effects of VegetationEffects of Vegetation

Trees near subscriber sites can lead to multipath fading

Multipath effects from the tree canopy are diffraction and scattering

Measurements in orchards found considerable attenuation values when the foliage is within 60% of the first Fresnel zone

Multipath effects highly variable due to wind

MMDS & LMDSMMDS & LMDS

Multipoint Distribution Service (MDS)Multipoint Distribution Service (MDS)

Multichannel multipoint distribution service (MMDS)– Also referred to as wireless cable– Used mainly by residential subscribers and small

businesses Local multipoint distribution service (LMDS)

– Appeals to larger companies with greater bandwidth demands

Advantages & Disadvantages of MMDSAdvantages & Disadvantages of MMDS

MMDS signals have larger wavelengths and can travel farther without losing significant power

Equipment at lower frequencies is less expensive

MMDS signals don't get blocked as easily by objects and are less susceptible to rain absorption

Low frequency results in less bandwidth

Advantages & Disadvantages of LMDSAdvantages & Disadvantages of LMDS

Relatively high data rates (Mbps range) Capable of providing video, telephony, and

data Relatively low cost in comparison with cable

alternatives Short range from base station requires a

large number to service a given area

802.16 Standards Development802.16 Standards Development

Use wireless links with microwave or millimeter wave radios

Use licensed spectrum Are metropolitan in scale Provide public network service to fee-paying

customers Use point-to-multipoint architecture with stationary

rooftop or tower-mounted antennas Provide efficient transport of heterogeneous traffic

supporting quality of service (QoS) Use wireless links with microwave or millimeter

wave radios Are capable of broadband transmissions (>2 Mbps)

802.16 Standards802.16 Standards

WiMAX (World-wide Interoperability for WiMAX (World-wide Interoperability for Microwave Access) Industry Group formed to Microwave Access) Industry Group formed to promote 802.16 standardspromote 802.16 standards

IEEE 802.16 Protocol ArchitectureIEEE 802.16 Protocol Architecture

Protocol ArchitectureProtocol Architecture

Physical and transmission layer functions:– Encoding/decoding of signals– Preamble generation/removal– Bit transmission/reception

Medium access control layer functions:– On transmission, assemble data into a frame

with address and error detection fields– On reception, disassemble frame, and perform

address recognition and error detection– Govern access to the wireless transmission

medium

Protocol ArchitectureProtocol Architecture

Convergence layer functions:– Encapsulate PDU (protocol data unit) framing of

upper layers into native 802.16 MAC/PHY frames

– Map upper layer’s addresses into 802.16 addresses

– Translate upper layer QoS parameters into native 802.16 MAC format

– Adapt time dependencies of upper layer traffic into equivalent MAC service

802.16 Protocols in Context802.16 Protocols in Context

IEEE 802.16.1 Bearer ServicesIEEE 802.16.1 Bearer Services

Digital audio/video multicast Digital telephony ATM Internet protocol Bridged LAN Back-haul Frame relay

IEEE 802.16.1 Frame FormatIEEE 802.16.1 Frame Format

Header - protocol control information– Downlink header – used by the base station– Uplink header – used by the subscriber to convey

bandwidth management needs to base station– Bandwidth request header – used by subscriber to request

additional bandwidth Payload – either higher-level data or a MAC control

message CRC – error-detecting code

MAC Management MessagesMAC Management Messages

Uplink and downlink channel descriptor Uplink and downlink access definition Ranging request and response Registration request, response and acknowledge Privacy key management request and response Dynamic service addition request, response and

acknowledge Dynamic service change request, response, and

acknowledge Dynamic service deletion request and response Multicast polling assignment request and response Downlink data grant type request ARQ acknowledgment

802.16 Physical Layer802.16 Physical Layer

Upstream Transmission– Uses a DAMA-TDMA (Demand Assignment Multiple

Access-Time Division Multiple Access) technique– Error correction uses Reed-Solomon code– Modulation scheme based on QPSK

Continuous downstream mode – For continuous transmission stream (audio, video)– Simple TDM scheme is used for channel access– Duplexing technique is frequency division duplex (FDD)

Burst downstream mode– Targets burst transmission stream (IP-based traffic)– DAMA-TDMA scheme is used for channel access– Duplexing techniques are FDD with adaptive modulation,

frequency shift division duplexing (FSDD), time division duplexing (TDD)

802-16 Data Rates in Mbps802-16 Data Rates in Mbps

Mobile IP and Wireless Mobile IP and Wireless Application ProtocolApplication Protocol

Chapter 12

Mobile IP UsesMobile IP Uses

Enable computers to maintain Internet connectivity while moving from one Internet attachment point to another

Mobile – user's point of attachment changes dynamically and all connections are automatically maintained despite the change

Nomadic - user's Internet connection is terminated each time the user moves and a new connection is initiated when the user dials back in– New, temporary IP address is assigned

Operation of Mobile IPOperation of Mobile IP

Mobil node is assigned to a particular network – home network

IP address on home network is static – home address

Mobile node can move to another network – foreign network

Mobile node registers with network node on foreign network – foreign agent

Mobile node gives care-of address to agent on home network – home agent

Mobile IP ScenarioMobile IP Scenario

Three Basic Capabilities of Mobile IPThree Basic Capabilities of Mobile IP

Discovery – mobile node uses discovery procedure to identify prospective home and foreign agents

Registration – mobile node uses an authenticated registration procedure to inform home agent of its care-of address

Tunneling – used to forward IP datagrams from a home address to a care-of address

Discovery ProcessDiscovery Process

Mobile node is responsible for ongoing discovery process– Must determine if it is attached to its home

network or a foreign network Transition from home network to foreign

network can occur at any time without notification to the network layer

Mobile node listens for agent advertisement messages issued by foreign agents– Compares network portion of the router's IP

address with the network portion of home address

Agent SolicitationAgent Solicitation

Foreign agents are expected to issue agent advertisement messages periodically

If a mobile node needs agent information immediately, it can issue ICMP router solicitation message– Any agent receiving this message will then issue

an agent advertisement

Move DetectionMove Detection

Mobile node may move from one network to another due to some handoff mechanism without IP level being aware– Agent discovery process is intended to enable

the agent to detect such a move Algorithms to detect move:

– Use of lifetime field – mobile node uses lifetime field as a timer for agent advertisements

– Use of network prefix – mobile node checks if any newly received agent advertisement messages are on the same network as the node's current care-of address

Co-Located AddressesCo-Located Addresses

If mobile node moves to a network that has no foreign agents, or all foreign agents are busy, it can act as its own foreign agent

Mobile agent uses co-located care-of address– IP address obtained by mobile node associated with

mobile node's current network interface Means to acquire co-located address:

– Temporary IP address through an Internet service, such as DHCP

– May be owned by the mobile node as a long-term address for use while visiting a given foreign network

Registration ProcessRegistration Process

Mobile node sends registration request to foreign agent requesting forwarding service

Foreign agent relays request to home agent Home agent accepts or denies request and

sends registration reply to foreign agent Foreign agent relays reply to mobile node Registration Security

– Mobile IP designed to resist attacks– For message authentication, registration request

and reply contain authentication extension for mobile-home, mobile-foreign and foreign-home

TunnelingTunneling

Home agent intercepts IP datagrams sent to mobile node's home address– Home agent informs other nodes on home network that

datagrams to mobile node should be delivered to home agent

Datagrams forwarded to care-of address via tunneling. Encapsulated in outer IP datagram– IP-within-IP – entire IP datagram becomes payload in new

IP datagram– Minimal encapsulation – new header is inserted between

original IP header and original IP payload– Generic routing encapsulation (GRE) – developed prior to

development of Mobile IP

Mobile IP EncapsulationMobile IP Encapsulation

Wireless Application Protocol (WAP)Wireless Application Protocol (WAP)

Open standard providing mobile users of wireless terminals access to telephony and information services– Wireless terminals include wireless phones,

pagers and personal digital assistants (PDAs)– Designed to work with all wireless network

technologies such as GSM, CDMA, and TDMA– Based on existing Internet standards such as IP,

XML, HTML, and HTTP– Includes security facilities

WAP InfrastructureWAP Infrastructure

WAP Protocol StackWAP Protocol Stack

WAP Programming ModelWAP Programming Model

Wireless Markup Language (WML) Wireless Markup Language (WML) FeaturesFeatures

Text and image support – formatting and layout commands

Deck/card organizational metaphor – WML documents subdivided into cards, which specify one or more units of interaction

Support for navigation among cards and decks – includes provisions for event handling; used for navigation or executing scripts

WMLScriptWMLScript

Scripting language (similar to HTML) for defining script-type programs in a user device with limited processing power and memory

WMLScript capabilities:– Check validity of user input before it’s sent– Access device facilities and peripherals– Interact with user without introducing round trips to origin

server WMLScript features:

– JavaScript-based scripting language– Procedural logic– Event-based– Compiled implementation– Integrated into WAE

Wireless Application Environment Wireless Application Environment (WAE)(WAE)

WAE specifies an application framework for wireless devices

WAE elements:– WAE User agents – software that executes in

the wireless device– Content generators – applications that produce

standard content formats in response to requests from user agents in the mobile terminal

– Standard content encoding – defined to allow a WAE user agent to navigate Web content

– Wireless telephony applications (WTA) – collection of telephony-specific extensions for call and feature control mechanisms

WAE Client ComponentsWAE Client Components

Wireless Session Protocol (WSP)Wireless Session Protocol (WSP)

Transaction-oriented protocol based on the concept of a request and a reply

Provides applications with interface for two session services:– Connection-oriented session service – operates

above reliable transport protocol WTP– Connectionless session service – operates

above unreliable transport protocol WDP

Connection-mode WSP ServicesConnection-mode WSP Services

Establish reliable session from client to server and release

Agree on common level of protocol functionality using capability negotiation

Exchange content between client and server using compact encoding

Suspend and resume a session Push content from server to client in an

unsynchronized manner

WSP Transaction TypesWSP Transaction Types

Session establishment – client WSP user requests session with server WSP user

Session termination – client WSP user initiates termination

Session suspend and resume – initiated with suspend and resume requests

Transaction – exchange of data between a client and server

Nonconfirmed data push – used to send unsolicited information from server to client

Confirmed data push – server receives delivery confirmation from client

Wireless Transaction Protocol (WTP)Wireless Transaction Protocol (WTP)

Lightweight protocol suitable for "thin" clients and over low-bandwidth wireless links

WTP features– Three classes of transaction service

Class 0 provides unreliable datagram service Class 1 provides reliable datagram service Class 2: provides request/response service

– Optional user-to-user reliability: WTP user triggers confirmation of each received message

– Optional out-of-band data on acknowledgments– PDU concatenation and delayed acknowledgment to

reduce the number of messages sent– Asynchronous transactions

Examples of WTP OperationsExamples of WTP Operations

Wireless Transport Layer Security Wireless Transport Layer Security (WTLS) Features(WTLS) Features

Data integrity – ensures that data sent between client and gateway are not modified, using message authentication

Privacy – ensures that the data cannot be read by a third party, using encryption

Authentication – establishes authentication of the two parties, using digital certificates

Denial-of-service protection – detects and rejects messages that are replayed or not successfully verified

WTLS Protocol StackWTLS Protocol Stack

WTLS consists of two layers of protocols– WTLS Record Protocol – provides basic security services to

various higher-layer protocols– Higher-layer protocols:

The Handshake Protocol The Change Cipher Spec (encryption & hash algorithm, crypto

attributes, etc…) Protocol The Alert Protocol

WTLS Record Protocol OperationWTLS Record Protocol Operation

Phases of the Handshake Protocol Phases of the Handshake Protocol ExchangeExchange

First phase – used to initiate a logical connection and establish security capabilities

Second phase – used for server authentication and key exchange

Third phase – used for client authentication and key exchange

Forth phase – completes the setting up of a secure connection

Wireless Datagram Protocol (WDP)Wireless Datagram Protocol (WDP)

Used to adapt higher-layer WAP protocol to the communication mechanism used between mobile node and WAP gateway

WDP hides details of the various bearer networks from the other layers of WAP

Adaptation may include:– Partitioning data into

segments of appropriate size for the bearer

– Interfacing with the bearer network

Wireless Control Message Protocol Wireless Control Message Protocol (WCMP)(WCMP)

Performs the same support function for WDP as ICMP does for IP

Used in environments that don’t provide IP bearer and don’t lend themselves to the use of ICMP

Used by wireless nodes and WAP gateways to report errors encountered in processing WDP datagrams

Can also be used for informational and diagnostic purposes

introduction to mobile communications tcom 552, lecture #10 hung nguyen, ph.d. 13 november, 2006

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